On first sight our current scientific understanding of the universe seems consistent with a physicalist viewpoint, so what’s the problem? Why introduce novel ideas without any objective evidence to warrant such a move?

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Well, science doesn’t just collect evidence. The whole endeavour starts by observing phenomena in the world that require explanation, and then asking relevant questions. Only then do we formulate a hypothesis and devise experiments to collect evidence.

The phenomena to be explained here are those of the mind; specifically qualia, or the qualitative nature of experience. This covers sensory experience, (for example, what it is like to see the colour red), and can arguably be extended to include cognitive phenomenology, or what it is like have thoughts, beliefs, desires or anything else.

Imagine trying to explain why one person likes broccoli and another does not. We might talk about the physical mechanics of taste and differences in sensitivity. That’s a useful answer for many reasons, but is it really telling us about the subjective contents of the mind?

We might have discerned how and why the subject is experiencing an unpleasant taste, but that’s simply because we are able to liken their experience to those of our own (for example, we might imagine what it’s like to taste something that’s too bitter).

We still have no idea how the broccoli tastes to them if we like it ourselves, because the experience in question isn’t tractable by analogy, just like we would not be able to explain the qualitative experience of sight to a blind person or hearing to the deaf.

This is related to what philosophers call the explanatory gap, and in itself it presents a potential problem for physicalism. Just how do you explain how objective physical causes, like the firing of neurons in the brain, give rise to subjective personal experience?

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Physicalist responses include reductive ideas like eliminativism where conscious phenomena are entirely imaginary (mind states simply are brain states and nothing more), and non-reductive ones like emergentism, where conscious phenomena emerge as novel things in the world from lower-level physical facts (much like the wetness of water emerges from molecules of H2O).

However, most non-reductive versions of physicalism are epiphenomenal in nature, meaning that consciousness is an unnecessary by-product of physical activity in the brain. This view is consistent with physicalist ideas about the non-existence of free will, because although brain states cause mind-states, mind states cannot cause brain states in return, but it raises questions regarding how and why consciousness evolved in the first place.

Another argument against materialism, and one that seeks to counter eliminativism and epiphenomenalism, is the knowledge argument, also known as Mary’s room.

Imagine a great scientist called Mary who has lived her whole life in a black and white room with only black and white objects (ignore the practical difficulties of the scenario, this is a thought experiment!). Mary has access to all the scientific knowledge of an advanced civilization, so she knows absolutely everything there is to know about colours vision.

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Now imagine that Mary is allowed to leave the room, and sees the colour red for the first time. The argument says that despite knowing everything about the physical world – all it’s properties and laws – Mary has still learnt a new fact about the world, that being what it’s like to see red. According to the argument, this shows that qualia are both real and non-physical.

I would also argue that this thought experiment suggests that consciousness is causally efficacious, as Mary could be instructed to perform an action based on whether she knows what it’s like to see red. (Note however that this does not count as evidence for free will).

Again in response, physicalists might say that Mary hasn’t actually learnt any new facts about the world, but just learnt a new skill. Others might argue that a truly comprehensive understanding of the physical world would include such knowledge in the first place, although this opens physicalism up to alternative monistic approaches such as the various flavours of panpsychism.

My main point is that these issues are not resolved, and that the physicalist position is far from set in stone. It may be the dominant view, but it is not the only one. And given the huge gaps in our scientific understanding at the most fundamental level of microphysics, it’s not even the most likely. The odds are even because it’s an entirely open question.

Next up, maybe I’ll write some words on what I think are sometimes unspoken motivations in the physicalist viewpoint, and how and why it has become the dominant position amongst scientists and intellectuals. On the other hand I might go into the science itself to illustrate just where those gaps in our understanding are widest and deepest.